My 17yo has now got braces, and the first week post-surgery (8 teeth removed) and when her braces were first put on, her biggest frustration was not being able to eat anything *other* than cold, milky foods. She's not a big fan of dairy products to start with, so her irritation was pretty high. She did drink some of the prepared smoothies, and made some of her own, but the non-stop-cold diet really got on her nerves.
My kid found that she really liked over-cooked carrots, mushed with ranch dressing. She was really missing her fave snack: raw carrots dipped in ranch dressing. She said they tasted different, but they were great. I see no reason why the same thing can't be pureed. We also made apple pie filling by chopping apples finely and cooking them with cinnamon in a little butter (no sugar needed in cooked apples in her opinion), because she loves apples.
Advice piece #1: get a LOT of the small-jar containers that fit on your blender (get a blender if you don't have one, and make sure it's the kind that has the small jars). You will find that you get bored out of your mind with the 'big batch' of whatever you made and you'll be looking for smaller portions of more variety very quickly.
Cook oatmeal in more water than it calls for, and for longer, so it breaks down completely. No puree required, and you can cook things into it (like chopped dates and apricots, peeled and cored apples or pears, because they all collapse completely) that have extra fibre and other flavours (like vanilla, cinnamon or even chocolate... mmmm... chocolate oatmeal <Grin>) that don't make it any thicker. If you make it thin enough, you may find (like the Indians and Mexicans) that it makes quite a refreshing cold drink.
You can also make 'nut milk' by pureeing and then straining a cup of raw or toasted nuts (almonds are particularly good, but I'm a macadamian and cashew fan, too) or fresh or dried coconut with 2 cups of boiling water (keep your hands away from any openings in the top of the blender. Puree for a lot longer than you think is reasonable, and you'll have very little stuff in the strainer. This is a high-fat product, but the fats are healthy and you may find it difficult to get enough into your body and that you're constantly hungry. This can help -- it's nutrient and calorie rich in liquid form.
Remember that a lot of what you're being offered has a lot of sugar and a lot of fat in it, and focus on those vegetables that are palatable when cooked more (like beets or potatoes or carrots, parsnips, carmelized onions...mmmm) and can easily be made into or added to, purees. Spinach -- in fact, most green foods -- turns into sand, somehow, when pureed, so just don't. Ew, gawd, please just don't try spinach. Even when it's cooked, it's just not food when pureed.
You don't need to emphasize protein much, because it's in practically everything, but you do need to stay aware of how much of what you eat is simple carbs -- like Ensure. That stuff is really quite a gross collection of sugared yuk that isn't much better than a vitamin pill and a glass of strawberry milk, with added sugar. Resist the urge to thin everything with milk or juice, as both have a lot of sugar and no fibre.
Thin savoury things (like pizza... I've heard from several people that it's great blended!) with chicken or vegetable stock, flat beer, wine (mmmm, wine with mushroom soup!), coffee or tea (both add a subtle richness to many kinds of food, I use them in soups and stews regularly) or thinish salad dressings like vinegarettes when pureeing -- for variety of flavour as much as anything else.
Thin sweet things (like smoothies, fruit soups, cheesecake -- don't knock that until you try it, ma'ma!) with tea, your thin-cooked oatmeal thing from above, water with a little vanilla added (water will dilute the flavour a bit, might as well add some back in!), fresh squeezed orange, lime or lemon juice (commercially-made 'unsweetened' oj has lots of added sugar, because it's a 'process' not an 'ingredient' so it doesn't need to be labelled! grrr, FDA!), chocolate milk, regular milk, nut milk, or coconut milk (make yourself or canned --avoid the kind with metabisulfide in the ingredients). Avoid commercially-prepared alternative 'milks' because they all add a bucket of sugar, and tend to have had a lot of the healthy fats removed before processing, because they're worth more to sell as oil and everyone knows that fat in food is immoral.
Make sure you're eating a variety of colours (at least before they're blended!) and what would look like a balanced diet if it weren't in the blender.
You may find that the syringe and tube you're getting are wider than you expect, enabling you to eat thicker foods than you'd think possible. You never know.